Reproducer



L. L. JONES Jan, 5, 1932.

REPRODUC ER Filed March 28, 1929 5 e n we J mL V Y we 1 S e L Patented Jan. 5, 1932 UNITED STATES PATENT OFFICE BEPRODUCER Application fled larch 28, 1928. Serial No. 850,732.

This invention relates to reproducers and more particularly to loud speakers of the electro-dynar'nic type.

A popular reproducer used with radio receiving sets is the electro-dynamic speaker. This type of speaker employs a field winding through which uni-directional current is passed in order to create an intense and steady magnetic field in which an armature 1o coil carrying the si nal current is vibrated. To energize the fiel of the speaker requires a considerable amount of energy, and for the economical and convenient provision of the necessary field exciting ener I find it ie feasible to separate each of a p urality of pulsating signal energies into its steady component and signal components, and to utilize the steady component for energizing the field of the reproducer. The foregoing method, and the circuits adapted for the practice thereof, are not claimed herein, being disclosed and claimed in a copending divisional application Serial No. 350,730, filed concurrently therewith.

While the foregoing method may be applied in a number of ways, some of which will be described more in detail later, I am more especially interested'in its application to receiving circuits of a common type which 30 employ an audio frequency power sta e between the receiver itself and the repro ucer. The power stage is usually ener 'zed at a direct potential which is considera ly higher than that needed to energize the amplifier tubes of the receiver. Inasmuch as it ordinarily is convenient to employ a single source of direct energy for the entire receiving system it then becomes necessary to reduce the voltage of the source before applying it to the anodes of the amplifier tubes. To obtain the desired reduced voltage and to simultaneously energize the field of the reproducer without wasting energy, I feed the anode current from the source to the amplifier through a field coil of the reproducer, thereby obtaining one of the exciting energies.

In a typical receiver the foregoing mode of energizatlon of the reproducer field provides, say, 6 watts of energy. The field needed is so intense that ordinary speakers of this type dissipate, say, 12 watts of energy for field energizatlon. It is possible to provide the necessary field by using an increased number of lower resistance field windings, and so to o erate the speaker on 6 watts of energy, but t e owth in size, weight, and cost of the spea er is so rapid, when the available energy is decreased, that it is much more desirable and commercially practicable to provide the greater rather than the lesser amount of energy.

A further feature of my invention resides in the provision of even the additional field energy by utilizing waste energy. The power stage of the receiver employs the maximum anode potential available from the direct current source, and requires a correspondingly hi h bias otential, which heretofore has been obtained rom the flow of the anode current of the power stage through a fixed resistance. Instead of wasting this energy, I use it to further excite the speaker field. While a lower potential difierence is here available than in the case of the potential reduction applied between the direct current source and the radio frequency amplifier, the current is comspeaker field. By utilizing a novel reproducer both waste energies may be employed togeth er, and such a reproducer, especially adapted for use in receiving circuits as previously set forth, constitutes the subject and the object of the resent invention.

To t e accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the reproducer elements and their relation one to the other, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing showing a wiring diagram for a broadcast receiver employing my novel reproducer.

Referring to the drawing, there is a suitable antenna or signal collectln circuit D, the energy picked up by which 18 amplified in a radio frequency amplifier E, after which it is rectified in any suitable detector F in order to make available the audio fre uency eomonent thereof, which then may e amplified m an audio frequency amplifier here exemplified by a push-pull power stage G, the output from which is translated in an electro-dynamic reproducer H. The entire receiving system'is ener d from a source of direct energy generafi y indicated at J, the latter 00m rising a power line transformer K, a rectifier L, and a filter M. The details of the radio frequency am lifier and detector, and the wiring for the lament heatln currents of the tubes, have all been omitted in order to simplify the diagram.

The power stage G necessitates an anode voltage of the order of magnitude of 250 to.

450 volts and, consequently, the power source J is designed to supply this voltage. The tubes in the amplifier need only be supplied with an anode voltage of the or er of magnitude of 100 volts, and it has been customary heretofore to obtain the necessaryreduction in voltage by dissipating energy in a fixed resistance. Now, in accordance with my invention, the anode current for the amplifier E is fed from the positive side 20 of the power source, by way of a lead 22, through the field coil 24 of the speaker H, and thence to the am lifier E.

y invention also involves a novel and very effective volume control for the receiver, but this will not be described in detail herein, inasmuch as it is disclosed and claimed in my copending application already referred to. Briefly considered, it ma be mentioned that there is a volume contro ing circuit including a fixed resistance 28 and a variable resistance 26 connected between the anode supply lead of the am lifier E, and the positive terminal of the ias ng resistance 32, the other terminal of which is connected to the negative side 30 of the direct current source. In this manner the volume control circuit forms an additional return path from the speaker coil 24 for field energizing current auxiliary to the anode current. When the resistance of the volume control circuit is lowered the current flow through the coil 24 is increased, and the potential dro thereacross is increased, thereby reducing t e anode potential applied to the amplifier, and so reducing its sensitivity. Meanwhile, the total current flow through the reproducer is augmented, rather than diminished as would be the case were no auxiliary magnetizing current provided. The increased total current flows through the biasin resistor 32, and thereby serves to increase the negative bias potential on the tubes of the amplifier, which affects the sensitivity of the amplifier in the proper direction, and at the same time obviates any possibility of a local signal over-running the bias on the control electrodes of the tubes.

It is customary in present receivers to employ electrode potentials on thedetector tube which are quite different from those employed on the amplifier tubes. This condition may, if desired, be accommodated by the provision of a potentiometer resistance 40, at suitable tapping points on which leads ar ge taken to the electrodes of the detector tll An electro-dynamic s aker requires an intense magnetic field. ith a iven amount of energy available, it is possi le to desi the fiel winding for the roper fie d strength. However, the num r of turns and the cross sectional area of each, and, consequently, the weight, the size, and the cost of the aker, increase enormously with a decrease in available power. A speaker designed to operate on 12 watts of field energy may be manufactured for about half the cost of a s eaker designed to operate on, say 6 watts o field energy. In an averzzfie set the field energization obtained by already described expedient is, say, 6 'watts. It is, therefore, desirable to augment the field energization, if ossible, and my invention makes this possi le b the rovision of a reproducer wlth a fiel whic is excited by a plurality of separate exciting circuits arranged to be independently energized from a lurality of immediate sources of ener y. ore specifically, I provide an electroynamic speaker having a plurality of field windings, instead of a single field winding, so that an additional field winding may be energized directly from the power box, as

is indicated by the coil 41 in the wirin diagram, even tho the applied potential is far different from that applied to the winding 24.'

However, the primary object of my invention is to make it possible to completely open.

ate an electro-dynamic speaker b the uti tion of waste energy. It should lie noted that the ush-pull power stage G requires direct ano e current in excess of that required b the radio frequency amplifier tubes, but it is not desirable to feed this current through a speaker field coil on its. way to the power stage G because the maximum voltage obtained from the source J is usuall the proper operating voltage for the type of power tube being used. In fact, the anode voltage for the power stage is frequently taken, as is indicated at 21 in the wiring diagram, from an intermediate tap on the filter M While the power stage uses an anode volt-' age which is relatively high, say 450 volts, the control electrodes thereof are biased nega tively to a commensurately high value, say 50 volts. This bias potential has heretofore been obtained by passing the steady component of the anode current of the pushull' stage through a resistor on its return pat to the negative side 30 of the source J, and then utilizing the potential drop across the resister for biasing the control electrodes of the power stage. I find that the energy consumed in this resistance is of the order of 6 watts, which is about the order of magnitude of the energy dissipated in'the coil 24, despite the much higher terminal voltage difference across the latter. In accordance with my invention the energy which-would otherwise'be dissipated in obtaining the desired bias potential for the power stage is utilized for energizing the field of the reproducer H.

Referring to the wiring diagram, there is another field coil 42 which is connected in series with the lead 44 from the cathodes of the tubes in the power stage, so that the anode to cathode current of the power stage flows through the coil 42 on its return to the negative terminal of the source J. An audio frequency bypass condenser 46 is arranged in shunt with the coil 42 in order to provide a control electrode to cathode path for audio frequency energy in the power stage, and for the further purpose of shunting audio frequency components in the anode current away from the speaker field coil. It is obvious that the power stage G need not be a push-pull stage, and in such case the necessity for the condenser 46 is, of course, increased. With a push-pull stage the anode current is inherently steadied to a considerable extent, but it is nevertheless desirable to provide the condenser 46 in order to take care of the doubleaudio frequency component which may otherwise be found present in the anode current lead. With windings 24 and. 42 I find it is readily possible to dispense with the coil 41, but it is retained in the diagram for the-purpose of illustration.

The winding for each of the speaker coils is preferably designed to best accommodate the particular energy with which it is to be excited. Of course, the design of the entire field winding is necessarily a compromise between the desire, on the one hand, for a maximum number of ampere turns for-a given amount of available energy, and a desire, on the other hand, to employ a reasonably small amount of material, particularly copper. In' the case here considered, the potential across and the current in the windings 24 and 42 are known, and, therefore, the respective desired resistances of these coils is readily ascertained. For example, winding 24 carries a relatively small amount of current, but this current is applied at a high potential, hence this coil is wound of a large number of turns of fine wire. On the ot or hand, the coil 42 carries a relatively large current which is applied at a relatively low potential, and this coil, therefore, is wound of a fewer number of turns of coarser wire. These remarks refer to the relative magnitudes of the several windings, rather than to their absolute dimensions. As to the latter,

little need be said for the design require ment is simply to obtain the maximum number of ampere turns, (which, in the absence of resistance, might be infinite,) without unduly enlarging the sizeand cost of the wind mgs.

The structural arrangement of the coils is merely a matter of convenience, and de' pends to someextcnt upon the design of the core or magnetic circuit of the particular reproducer. Generally speaking, -I consider it preferable to wind each of the coils as an integral unit which just fits into the core structure, and to position the coils alongside of each other, that. is, end to end.

In the arrangement here set forth the speaker field is energized by the direct com ponents of the anode currents of the amplitier and of the power stage, and such an ar-- rangement is particularly desirable in practice because some 10 to 12 watts of energy are thus provided, which is sufficient for economical construction without the energy being supplemented by energy fed directly from the same or a different direct current source, for example,-the volume control circuit energy in the circuit here illustrated, or the energy in coil 41. However, the utilization of these two waste energies was not only unknown heretofore, but was impossible of accomplishment because there was never available an electrodynamic speaker having two completely independent and unconnected field coils, one consisting of a large number of turns 'of fine wire, and the other consisting of a small number of turns of coarse wire.

It will be apparent that while I have shown and described my invention in the preferred form, many changes and modifications may be made in the reproducer disclosed without departing from the spirit of the invention, defined in the following claims.

In the claims I shall refer to the windings as adapted-to be energized from different immediate sources of energy, although in the very circuit illustrated the energization ultimately is from a single power line because the energies differ in potential and current magnitudes.

I claim:

1. In combination, speaker having a movable armature coil adapted for energization by audio frequency energy, and having a plurality of independent stationary field windings one of which consists of a large number of turns of fine wire, while another consists of a small numlife an electro-dynamie ber of turns of coarse wire, an immediate an immediate source of direct current at relatively low potential connected to the second of said windings, said windings each being.

designed for optimum practical utilization of the particular energies by which they are excited.

2. In combination, an electro-dynamic speaker having a movable armature coil adapted for energization by audio frequenc energy, and having a plurality of indepen ent stationary field windings one of which consists of a large number of turns of fine wire, while another consists of a small num- -ber of turns of coarse Wire, an immediate source of direct current at relatively high potential connected to the first Winding, and an immediate source of direct current at relatively low potential connected to the second of said windings, said windings each being designed for optimum practical utilization and for approximately equal dissipation of the articular energies by which they are excite Signed at New York, in the county of New York and State of New York, this 27th day of March, A. D. 1929.

LESTER L. JONES. 

